Reference signal configuration

ABSTRACT

A wireless transmit/receive unit (WTRU) is configured to receive a reference signal of a first type. The reference signal of the first type is other than a cell specific reference signal (CRS), an Multicast Broadcast Single Frequency Network (MBSFN) reference signal or a demodulation reference signal (DM-RS). Reference signals of the first type are received in resource elements other than resource elements used for a physical broadcast channel (PBCH), a primary synchronization signal or a secondary synchronization signal. The WTRU is configured to receive a radio resource control message indicating a subframe position in which the reference signal of the first type is transmitted and a periodicity of a transmission of the reference signal of the first type, and a number of antenna ports for a transmission of the reference signal of the first type.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/768,033, filed Apr. 27, 2010, which claims the benefit of U.S.provisional application No. 61/173,054 filed Apr. 27, 2009; U.S.provisional application No. 61/219,218 filed Jun. 22, 2009; U.S.provisional application No. 61/233,723 filed Aug. 13, 2009; and U.S.provisional application No. 61/234,018 filed Aug. 14, 2009, which areincorporated by reference as if fully set forth herein.

FIELD OF INVENTION

This application is related to wireless communications.

BACKGROUND

It is expected that the overall performance of positioning for long termevolution (LTE) will need to be as good as or better than that possiblefor other access types due to the increasing level of regulatoryrequirements in some regions and increasing demands imposed by newlocation service (LCS) applications.

To support these requirements, explicit positioning support should bedefined for LTE in a manner compatible with and capable of supportingthe emerging 3^(rd) Generation Partnership Project (3GPP) control planesolution and the secure user plane location (SUPL) solution in openmobile alliance (OMA). The overall objective should be to achieve paritywith or even surpass the capabilities and performance currently providedfor other wireless access types including Global System for Mobilecommunications (GSM), Wideband Code Division Multiple Access (WCDMA),CDMA2000 1×RTT and CDMA2000 EV-DO.

Moreover, the positioning capabilities and features in association withLTE may support: wireless transmit/receive unit (WTRU)-based andWTRU-assisted observed time difference of arrival (OTDOA) methods,Assisted Global Navigation Satellite System (A-GNSS) methods, enhancedcell identification (ECID), and other methods.

For LTE, the WTRU time difference measurements for the OTDOA method maybe based on one or more reference signals (RS) from the serving and/orneighbor cells. The RS may be either the existing Common RS (CRS) and/ora newly designed Positioning RS (PRS). The CRS and PRS may be usedindividually or in combination by the WTRU to derive the measuredmetrics. When using PRS, measurement in more than one subframe (called apositioning subframe) may be needed to accumulate enough energy toobtain one measurement sample for one or more specific neighbors.

Various issues may exist with using PRS for positioning measurements.

One issue applicable to both LTE frequency division duplexing (FDD) andtime division duplexing (TDD) modes, but particularly a problem in a TDDsystem where a limited number of downlink (DL) subframes is available,is the availability of N consecutive subframes to derive a measurement.

Another issue may relate to the paging mechanism. In LTE Release 8, amechanism for paging WTRUs has been defined for WTRUs in idle mode andin connected mode. WTRUs periodically monitor the physical downlinkcontrol channel (PDCCH) for downlink (DL) assignments masked with apaging radio network temporary identifier (P-RNTI). On a condition thatthe assignment is detected, the WTRU demodulates the assigned physicaldownlink shared channel (PDSCH) resource blocks (RBs) and decodes thepaging channel (PCH). This process is called monitoring a pagingchannel.

In idle mode, a WTRU monitors a paging channel to detect incoming calls,system information changes, and Earthquake and Tsunami Warning System(ETWS) notifications for ETWS capable WTRUs. The specific paging frame(PF) and subframe within that PF (a paging occasion (PO)) that the WTRUmonitors are determined based on the WTRU identity (ID) and twoparameters specified (directly or indirectly) by the network: pagingcycle length (in frames) and the number of paging subframes per pagingcycle. A WTRU may receive two paging cycle lengths, a cell-specific one(defaultPagingCycle) and a WTRU-specific one; in idle mode, it uses thesmaller of the two. From the network perspective, there may be multiplePOs within a PF (i.e., more than one subframe may carry PDCCH maskedwith a P-RNTI), but the WTRU is only required to monitor one PO per PF,and this PO is determined by the parameters specified above, andprovided to the WTRU via broadcast system information and/or dedicatedsignaling information.

The PRS configuration may be such that an idle mode WTRU may be“blocked” from its POs if all of the following conditions are met: thePRS periodicity is less than or equal to the paging cycle (i.e., theminimum of the cell-specific and WTRU specific paging cycles); any ofthe frames containing the PRS correspond to the WTRU's PF; and any ofthe subframes used for the PRS correspond to the WTRU's PO subframe.

In connected mode, a WTRU monitors a paging channel and systeminformation block type 1 (SIB1) contents to detect system informationchanges, and ETWS notifications for ETWS capable WTRUs. The connectedmode WTRU does not need to monitor any specific PO. It simply must tryto receive pages at the same rate as a WTRU in idle mode using thecell-specific paging cycle. This rate is determined by a systeminformation block type 2 (SIB2) parameter “modificationPeriodCoeff”. Thenetwork will send system information change pages on all POs during amodification period of lengthmodificationPeriodCoeff×defaultPagingCycle.

The PRS configuration may be such that a connected mode WTRU may be“blocked” from at least some of its POs if all of the followingconditions are met: the PRS periodicity is less than or equal to thecell-specific paging cycle; any of the frames containing the PRScorrespond to any PF; and any of the subframes used for the PRScorrespond to any PO subframes.

Another issue may relate to the handling of PRS in subframes allocatedfor evolved Multicast Broadcast Multimedia Service (eMBMS). The eMBMSfeature introduces support for MBMS services into LTE networks. MBMStransmissions are carried over a multicast channel (MCH) that includesmulticast shared channel (MSCH), multicast control channel (MCCH), andmulticast traffic channel (MTCH). The MCH is mapped to a Physical MBMSChannel (PMCH) that is mapped to MBSFN allocated subframes. In Release 9eMBMS, the PMCH cannot be multiplexed with the PDSCH into the samesubframe. Although eMBMS is a LTE Release 9 feature, the configuration(i.e., the subframe allocation) of the MBSFN allocated subframes wasdefined for Release 8 to allow Release 8 WTRUs to know which subframesare allocated for MBMS service. In an MBSFN allocated subframe, aRelease 8 WTRU decodes the control region (first 1 or 2 symbols) toobtain acknowledgement and negative acknowledgement (ACK/NACK) anduplink (UL) grant information. In MBSFN allocated subframes, the CRSwill be present in the control region, but not in the other symbols ofthe subframe.

In MBMS allocated subframes, in non-control orthogonal frequencydivision multiplexing (OFDM) symbols, a different RS, the MBSFN RS,rather than the CRS, is used. MBSFN RSs are only defined for the case ofextended prefix, i.e., for the case of 6 symbols per timeslot. MBSFN RSsare transmitted in every resource block (RB) in the configured downlinkbandwidth in alternating resource elements (REs) in the 3^(rd) symbol ofeven numbered timeslots and the 1^(st) and 5^(th) symbols ofodd-numbered timeslots.

Another issue may relate to the handling of the PRS in subframescontaining other RS such as those currently being defined for LTE andLTE-A (LTE advanced). For the purpose of dual-layer beamforming andhigher order multiple-input multiple-output (MIMO), Multi-user MIMO(MU-MIMO) and Coordinated Multipoint Transmission (CoMP), additionalDemodulation Reference Symbols (DMRS) are being defined. For Release 9,the number of DMRSs will be 12 per RB, and may only be in RBs containingPDSCH, and not in the control region or in symbols containing the CRS.

For LTE-advanced (LTE-A), a total of 24 DMRSs per RB may be used andthese DMRS may also not occur in the control region or in symbolscontaining the CRS. The DMRS on different antenna ports may bemultiplexed by frequency division, code division or a combination offrequency and code division.

In addition to DMRS, LTE-A will be adding Channel State Information(CSI)-RS, located throughout the transmission bandwidth of the cell, toallow the WTRU to perform CSI measurements in support of CoMP andMU-MIMO, as well as to support up to 8 DL transmission antenna ports.

Methods and procedures are needed to support PRS in conjunction withWTRU OTDOA based positioning, MBMS, paging mechanisms, availablesubframes for allocation which may not be consecutive, subframescontaining system signals, and subframes containing RSs, in LTE andLTE-A networks.

SUMMARY

Methods and apparatus for supporting reference signals for positioningmeasurements are disclosed. Methods include subframe configuration,subframe structures, measurement opportunities using a set of downlinksubframes which are not all consecutive, handling of subframescontaining reference signals and system signals such as synchronizationsignals, paging occasions and Multicast Broadcast Multimedia Service(MBMS), and related control signaling between a long term evolution(LTE) network and a wireless transmit/receive unit (WTRU). Moreover,methods to resolve allocation conflicts arising between positioningreference signals and other reference signals are disclosed.

BRIEF DESCRIPTION OF THE DRAWINGS

A more detailed understanding may be had from the following description,given by way of example in conjunction with the accompanying drawingswherein:

FIG. 1 is an embodiment of a wireless communication system/accessnetwork of LTE;

FIG. 2 is an example block diagram of a wireless transmit/receive unitand a base station of LTE wireless communication system;

FIG. 3 shows an embodiment for placement of reference signals withrespect to resource elements;

FIG. 4 is a flow diagram of an example procedure for positioningreference signal determination and transmission; and

FIG. 5 is a flow diagram of another example procedure for positioningreference signal determination and transmission.

DETAILED DESCRIPTION

When referred to hereafter, the terminology “wireless transmit/receiveunit (WTRU)” includes but is not limited to a user equipment (UE), amobile station, a fixed or mobile subscriber unit, a pager, a cellulartelephone, a personal digital assistant (PDA), a computer, or any othertype of device capable of operating in a wireless environment. The WTRUmay include a home Node-B, an evolved Node-B, a home evolved Node-B, arelay or any other type of moveable device that may require positioningsupport.

When referred to hereafter, the terminology “base station” includes butis not limited to a Node-B, home Node-B, an evolved Node-B, a homeevolved Node-B, a relay, a site controller, an access point (AP), or anyother type of interfacing device capable of operating in a wirelessenvironment.

FIG. 1 shows a Long Term Evolution (LTE) wireless communicationsystem/access network 100 that includes an Evolved-Universal TerrestrialRadio Access Network (E-UTRAN) 105. The E-UTRAN 105 includes severalevolved Node-Bs (eNBs) 120. The WTRU 110 is in communication with an eNB120. The eNBs 120 interface with each other using an X2 interface. Eachof the eNBs 120 interface with a Mobility Management Entity(MME)/Serving GateWay (S-GW) 130 through an S1 interface. The MME/SGW130 may interface with an evolved serving mobile location center(E-SMLC) 135 for at least control plane positioning support and forsending location information to or receiving location information fromthe WTRU 110. The network 100 may include other entities (not shown)such as, but not limited to, a secure user plane location server.Although a single WTRU 110 and three eNBs 120 are shown in FIG. 1, itshould be apparent that any combination of wireless and wired devicesmay be included in the wireless communication system access network 100.

FIG. 2 is an embodiment of a block diagram of an LTE wirelesscommunication system 200 including the WTRU 110, the eNB 120, and theMME/S-GW 130. As shown in FIG. 2, the WTRU 110, the eNB 120 and theMME/S-GW 130 are configured to allocate and handle reference signals forpositioning measurements.

In addition to the components that may be found in a typical WTRU, theWTRU 110 includes a processor 216 with an optional linked memory 222, atleast one transceiver 214, an optional battery 220, and one or moreantennas 218. The processor 216 is configured to handle referencesignals for positioning measurements. The transceiver 214 is incommunication with the processor 216 and the antenna(s) 218 tofacilitate the transmission and reception of wireless communications. Incase a battery 220 is used in the WTRU 110, it powers the transceiver214 and the processor 216.

In addition to the components that may be found in a typical eNB, theeNB 120 includes a processor 217 with an optional linked memory 215,transceivers 219, and antennas 221. The processor 217 is configured toallocate and handle reference signals for positioning measurements. Thetransceivers 219 are in communication with the processor 217 andantennas 221 to facilitate the transmission and reception of wirelesscommunications. The eNB 120 is connected to the Mobility ManagementEntity/Serving GateWay (MME/S-GW) 130 which includes a processor 233with an optional linked memory 234.

Embodiments disclosed herein may be used separately or together.Embodiments may apply to time division duplexing (TDD) and frequencydivision duplexing (FDD). Certain examples may be chosen to illustrateTDD, but the embodiments are still applicable to both TDD and FDD unlessspecifically stated otherwise.

Disclosed herein are methods for allocating and handling referencesignals for positioning measurements. These reference signals may bedenoted as a positioning reference signal (PRS) herein. A PRS may bedefined, for example, as one or more symbols in a time and frequencygrid that are known to a signaling base station and a decoding WTRU. Theterm positioning may be extended to mean any signal defined to be usedfor measurements in support of positioning. The term positioning signalmay be used interchangeably with PRS. The PRS may be used for otherpurposes in accordance with the methods described herein.

The methods described herein are illustrated with respect to the PRS butare applicable to reference signals in general.

It is understood that the terminology “not mapped” and “punctured” areused interchangeably to refer to situations where the PRS may not usethe resource in question due to the presence of other signals, asdescribed herein.

Described herein are embodiments for allocation of PRS(s) in positioningsubframes.

In one embodiment, when the PRS(s) are in the same subframe as systemsignals such as, but not limited to, physical broadcast channel (PBCH),synchronization signals, paging signals, and other such system signals,the allocation of the PRS(s) respect the presence of those systemsignals. That is, the positioning resource blocks (RBs) will not beallocated to RBs allocated to the system signals.

FIG. 4 is a flow diagram of an example procedure 400 for positioningreference signal determination and transmission. In the example of FIG.4, if the PRS(s) may be allocated into a subframe that carries one ormore paging occasions (POs) for at least one WTRU, RBs for PRStransmission may be determined, 402. when the PRS(s) are in subframes inwhich synchronization signals (SS) (primary and secondary), or PBCH(i.e., master information block (MIB)) or important SIBs (such as SIB1)are present in one or more physical resource blocks (PRBs), the PRS(s)may not be mapped to those REs identified as carrying SS, P-BCH, SIB1,and other system signals, 404. Thus, PRS may be transmitted in the RBsfor PRS transmission excluding transmission in the identified REs, 406.

In another embodiment, if there are any Release 8 reference signals (RS)present in a physical resource block (PRB), then one or a combination ofoptions are available. In one option, PRS(s) may not be mapped to thoseREs that include Release 8 RS(s). In another option, PRS(s) may not bemapped to those REs that include legacy RS(s) in the downlink controlregion (in LTE Release 8 this means the first n OFDMA symbols, n=1, 2 or3). PRS(s) may be mapped to those REs that include a Release 8 RSoutside the downlink control region. In this manner, the WTRU mayperform channel estimation using received PRS(s) in order todetect/decode downlink data. In another option, PRS(s) may be mapped tothose REs that include Release 8 RS. In this option, the Release 8 RS(s)may be punctured in those REs. In this way, the WTRU may perform channelestimation using received PRS(s) in order to detect/decode downlink dataand control. In another option, Release 8 RS(s) may be incorporated aspart of the PRS(s) without impacting Release 8 functionality.

In another embodiment, the mapping of the PRS(s) in subframes containingsystem signals may be derived from the mapping used in the normalsubframes that do not contain these system signals. This mapping rulemay be known to the WTRU. No additional signaling may be needed toconvey the derivation to the WTRU since the mapping rule may be known tothe WTRU and the WTRU may perform the derivation.

In another embodiment, the allocated PRS region occurs over the centerbandwidth when the PRS measurement bandwidth is less than the DL systembandwidth in a positioning subframe.

In another embodiment, in the case where an RE may contain a Release 8demodulation RS (DRS) and may also contain a PRS, the DRS may not bepunctured by the PRS. The PRS is punctured.

In another embodiment, in the case where an RE may contain a Release9/10 demodulation RS (DMRS) and may also contain a PRS, the DMRS may notbe punctured by the PRS. The PRS is punctured.

In another embodiment, in the case where an RE may contain a ChannelState Information (CSI)-RS and may also contain a PRS, the RE maycontain the CSI-RS and the PRS may be punctured.

In another embodiment, in the case where an RE may contain a ChannelState Information (CSI)-RS and may also contain a PRS, the CSI-RS may bepunctured. The WTRU may use the PRS in this RE as part of its estimationof CSI.

FIG. 5 is a flow diagram of another example procedure 500 forpositioning reference signal determination and transmission. In theexample of FIG. 5., the PRS(s) may not be sent by a network node, e.g.,a base station, in a subframe in RBs carrying a physical downlink sharedchannel (PDSCH) with paging information. For example, on a conditionthat the PRS(s) may be allocated into a subframe that carries one ormore paging occasions (POs) for at least one WTRU, RBs for PRStransmission may be determined, 502, such that the PRS(s) may pre-emptand substitute RBs for PDSCH carrying regular traffic such as a trafficchannel (TCH) allocated in that subframe. However, any RB identified asbeing used for PDSCH carrying paging information may not carry thePRS(s), 504. Paging information may pertain to a PDSCH carrying a pagingchannel (PCH), a PDSCH carrying SIB1 or SIB2 system information, a PDSCHusing any form of signaling to reach either one or more WTRUs to informthem of pending paging messages, system information changes, publicwarning system (PWS) notifications, or other similar information, 504.Thus, PRS may be transmitted in the RBs for PRS transmission excludingtransmission in the identified PDSCH RBs, 506.

In another embodiment, the PRS(s) may not be sent by a network node,e.g., a base station, in one or more selected subframes carrying a PDSCHwith paging information. For example, a WTRU may not be required todecode and measure the PRS(s) in either all or some subframes containingat least one PDSCH carrying paging information. For example, a regularlyrepeating or a pseudo-random pattern in conjunction with the PRS(s)configuration may be used to disable PRS transmission for the purpose ofpaging decoding by the WTRU.

In another embodiment, PRS(s) transmission in given subframes, incertain POs, paging frame (PF) occurrences, or for certain RBs carryingPDSCH with paging information, is configured as a function of either PRSconfiguration parameters, such as PRS occurrence (i.e., startingsubframe number and periodicity of subframes containing PRS(s)) or PRSaccumulation mode (e.g., number of consecutive subframes containingPRS(s)), or discontinuous reception (DRX) cycles.

In another embodiment, on a condition that the PRS configuration is suchthat any idle mode WTRU may have all of its POs blocked by the PRS(s),and the WTRU specific DRX cycle is greater than or equal to the cellspecific DRX cycle, or the WTRU specific DRX cycle is not specified, thePRS(s) may not be transmitted during these POs. This ensures that allPOs are available to idle mode WTRUs, as well as to connected modeWTRUs.

In another embodiment, on a condition that the PRS configuration is suchthat any idle mode WTRU may have all of its POs blocked by the PRS, andthe WTRU specific DRX cycle is less than the cell specific DRX cycle,the PRS may not be transmitted during POs corresponding to PFsdetermined by the cell specific DRX cycle. This ensures that at leastsome POs will be available to the WTRU, and that connected mode WTRUsmay have all of their known POs available.

In another embodiment, in cases where a conflict exists between a PO forany WTRU and a PRS transmission, the paging transmissions may berestricted to the PDSCH transmissions outside of the RBs utilized forthe PRS.

In another embodiment, either all or a subset of the subframes allocatedor potentially allocated for paging are designated unavailable forPRS(s) regardless of whether they contain paging information (such asPDSCH carrying PCH) or not. PRS(s) may not be transmitted in theunavailable subframes. For example, subframes potentially allocated forpaging are currently subframes 0, 4, 5, and 9 in FDD, or 0, 1, 5, and 6in TDD. Designating all potentially allocated subframes in FDDunavailable for paging would mean disallowing PRS(s) in subframes 0, 4,5, and 9. In another example, if based on the paging parameters chosenby the network, if only one subframe is allocated, such as subframe 9,for POs (for any WTRU) in every nth frame, then PRS(s) would not beallowed in that one subframe (e.g., subframe 9) every nth frame or everymultiple of n frames (e.g., 2n frames) to prevent blocking. In anotherexample, if the PRS period is less than or equal to the DRX cycle, PRSmay be disallowed in the allocated or potentially allocated pagingsubframes (for example, subframes 0, 4, 5, and 9) in every n DRX cyclesto ensure that every WTRU may read its pages at least once every n DRXcycles. Further, the unavailable subframes may be pre-defined, e.g., bythe third generation partnership project (3GPP) standard, or signaled tothe WTRU.

In another embodiment, the PRS periodicity may be assigned values thatare not powers of 2 in terms of frames to reduce the frequency ofcollisions between PRS occurrences and POs. That is, collisions could nolonger occur on consecutive POs. In particular, selecting values for PRSperiodicity that share no common divisor with the DRX cycle lengths mayminimize the frequency of collisions. For example, while the DRX cyclelength may be 32, 64, 128, or 256, the PRS may instead be assignedvalues of 17, 33, 65, or 129. As another example, a non-integer numberof frames may also be used for the PRS period, for example, 161subframes which corresponds to 16.1 frames.

In another embodiment, the PDSCH carrying PCH may be allowed in RBs inany part of the cell transmission bandwidth of a subframe carryingPRS(s) that is not allocated for PRS(s), but not allowed in the celltransmission bandwidth of the subframe that is allocated for PRS(s). Asan example, if the cell transmission bandwidth is 20 MHz and the PRSallocation only uses the center 10 MHZ, then the PDSCH carrying the PCHmay be allowed in the 10 MHz not allocated for PRS(s) in the subframescarrying PRS(s).

It is noted that in Multicast Broadcast Single Frequency Network (MBSFN)allocated subframes, the first 1 or 2 symbols are always reserved forphysical downlink control channel (PDCCH) per LTE specifications. PRS(s)may not be transmitted in those symbols. In order to align with normalsubframes which may use the first 3 symbols for control, the 3^(rd)symbol may not be used for PRS in both normal and MBSFN allocatedsubframes. The methods and procedures described herein are notmaterially affected by these considerations.

In another embodiment, the PRS(s) may be allocated to subframes thatcarry Multimedia Broadcast/Multicast Service (MBMS) services, and/or maybe allocated to subframes that contain MBSFN RS(s) in either the entiresubframe, or one or more resource blocks (RBs) contained therein. In anon-limiting example, the MBMS service may be carried by a physicalmulticast channel (PMCH) which is mapped to MBSFN allocated subframesand the MBSFN RS is used.

In an illustrative example of this embodiment, in a positioning subframethat is also an MBSFN allocated subframe, the rules for MBSFN allocatedsubframes may be applied whether or not MBSFN RSs are transmitted. TheWTRU may assume that MBSFN RSs are transmitted and act accordingly basedon the PRS pattern specified for an MBSFN allocated subframe with MBSFNRS.

In another illustrative example of this embodiment, in a positioningsubframe, there is one PRS pattern transmitted that is the same in allsubframes with the exception of the symbols and/or resource elements(REs) that are punctured based on conflict with other RS transmissions,such as Cell Specific RS (CRS) or MBSFN RS.

In another illustrative example of this embodiment, in a positioningsubframe that is also an MBSFN allocated subframe, if some RBs containMBSFN RS and others do not, the normal subframe PRS pattern in the RBsthat do not contain MBSFN RS may be used as-is or with knownmodifications. For example, in a positioning subframe that is also anMBSFN allocated subframe, if some RBs contain MBSFN RSs and others donot, the normal subframe (depending on the broadcast number of PBCHports) PRS pattern in the RBs that do not contain MBSFN RSs may be used.In another example, in a positioning subframe that is also an MBSFNallocated subframe, if some RBs contain MBSFN RSs and others do not, thenormal subframe (for two PBCH ports, independent of the actual number ofPBCH ports) PRS pattern in the RBs that do not contain MBSFN RSs may beused. In yet another example, in a positioning subframe that is also anMBSFN allocated subframe, if some RBs contain MBSFN RS and others donot, the normal subframe (for four PBCH ports, independent of the actualnumber of PBCH ports) PRS pattern in the RBs that do not contain MBSFNRSs is used. In still another example, in a positioning subframe that isalso an MBSFN allocated subframe, if some RBs contain MBSFN RS andothers do not, the normal subframe PRS pattern in the RBs that do notcontain MBSFN RS is used, but the PRS is not punctured in the symbolsand/or REs where the CRS exists in the normal subframe.

In another illustrative example of this embodiment, in a positioningsubframe that is also an MBSFN allocated subframe, the PRS may not usesymbols and/or REs containing MBSFN RS. In one example, in a positioningsubframe that is also an MBSFN allocated subframe, for the case where anRE would contain an MBSFN RS and would also contain a PRS, the RE maycontain the MBSFN RS, and the PRS may be punctured. In another example,in a positioning subframe that is also an MBSFN allocated subframe, thePRS may not use symbols that are used by MBSFN RSs. In yet anotherexample, in a positioning subframe that is also an MBSFN allocatedsubframe, the normal subframe PRS pattern in MBSFN allocated subframesthat contain MBSFN RS may be used, but the PRS REs are not punctured inthe symbols and/or REs where the CRS exist in the normal subframe.Instead, the REs where the MBSFN RS exist are punctured. In a furtherexample, in a positioning subframe that is also an MBSFN allocatedsubframe, if some RBs contain MBSFN RS and others do not, in the RBscontaining MBSFN RS, the normal subframe PRS pattern may be used, butthe PRS REs are not punctured in the symbols and/or REs where the CRSexist in the normal subframe. Instead, the PRS(s) that would otherwisebe in the REs where the MBSFN RS exist are punctured.

In a further example, in a positioning subframe that is also an MBSFNallocated subframe, the normal subframe PRS pattern in MBSFN allocatedsubframes that contain MBSFN RS may be used, but the PRS REs are notpunctured in the symbols and/or REs where the CRS exist in the normalsubframe. Instead the PRS that would otherwise be in symbols where theMBSFN RS exist are punctured. An illustrative expression of the PRSpattern in the RBs containing the PRS may be shown as follows:For Δf=15 kHz:

k = 6m + (5 − l + v_(shift))mod 6 $l = \begin{Bmatrix}{3,4,5} & {{{if}\mspace{14mu} n_{s}{mod}\; 2} = 0} \\{1,2,3,5} & {{{if}\mspace{14mu} n_{s}{mod}\; 2} = 1}\end{Bmatrix}$ m = 0, 1, …  , 2 ⋅ N_(RB)^(PRS) − 1m^(′) = m + N_(RB)^(ma x, DL) − N_(RB)^(PRS)Note that the first 2 symbols are not used for PRS because they arereserved for the physical downlink control channel (PDCCH) and the3^(rd) symbol is not used since it contains the MBSFN RS. The sameexpression may be used in the case of 3 reserved control symbols. Alsonote that unlike PRS(s) in normal subframes, this expression isindependent of the number of PBCH antenna ports.

In yet a further example, as shown in FIG. 3, in a positioning subframethat is also an MBSFN allocated subframe, if some RBs contain MBSFN RSand others do not, in the RBs containing MBSFN RS, the normal subframePRS pattern may be used, but the PRS REs are not punctured in thesymbols and/or REs where the CRS exist in the normal subframe. Instead,the PRS that would otherwise be in symbols where MBSFN RS exist arepunctured. Physical Control Format Indicator Channel (PCFICH), PhysicalHybrid Automatic Repeat Request Indicator Channel (PHICH), and PhysicalDownlink Control Channel (PDCCH) are downlink control signals that mayexist in the downlink control region of a subframe.

In another embodiment, PRS(s) in support of positioning measurementscannot be allocated to subframes that carry MBMS services, and/or cannotbe allocated to subframes that contain MBMS RSs in the entire subframe,and/or cannot be allocated to subframes that contain MBSFN RS in atleast one or more RBs contained therein.

In an illustrative example of this embodiment, the WTRU is un-aware ofwhich MBSFN allocated subframes contain MBMS and/or carry MBSFN RS in atleast a portion or the entire subframe. The WTRU may perform positioningmeasurements assuming PRS(s) is always present in all allocationsindicated valid for PRS.

In another illustrative example of this embodiment, the WTRU is aware ofwhich MBFSN-allocated subframes contain MBMS and/or MBSFN RS, and doesnot schedule positioning measurements for those subframes. In anexample, the WTRU learns and builds the list of admissible MBSFNsubframes through any of the procedures described herein for determiningwhich subframes carry MBMS/MBSFN RSs.

In another embodiment, in the positioning subframe, the PRS(s) may besuperimposed (or overlaid) on downlink data and reference signals oronly on the downlink data resource elements (REs). The base station maystill transmit downlink data. However, the scheduled downlink datatransmission may use lower transmit power, lower modulation and codingscheme (MCS), smaller transport block and/or a restricted set ofresource blocks (RBs) than what the current link conditions would allowif the PRS(s) were not transmitted. The lowering of the downlink datarate via these methods allows for reliable data reception in thepresence of the increased interference due to the transmission of thepositioning signal. Also the base station may have leftover transmission(Tx) power to transmit the PRS(s) and this may also reduce interferenceof the data to the PRS(s).

The superposed PRS(s) may occupy the entire bandwidth of the LTEcarrier/cell in order to achieve the required accuracy of timedifference measurements and low signal+interference to noise ratios(SINR) detection threshold (such as −30 dB). The waveform of thesuperposed PRS(s) may be a CDMA type (spread spectrum) signal, OFDM(A)type signal or other type of signal.

In another embodiment, the primary synchronization signals (PSS) in LTERelease 8 occupies the central 62 subcarriers and may be extended to theentire bandwidth to be used as superposed PRS(s) as described herein.

In another embodiment, the secondary synchronization signals (SSS) inLTE Release 8 occupy the central 62 subcarriers and may be extended tothe entire bandwidth to be used as superposed PRS(s) as describedherein.

In another embodiment, some RBs in the downlink subframes may be definedto transmit the PRS(s) while using the remaining RBs for legacy type LTEdata transmission.

Disclosed herein are embodiments for positioning subframe allocation.

In one embodiment, when more than 1 downlink subframe may be used fortime aggregation of a single positioning measurement sample, thedownlink subframes used for positioning signals are not required to beconsecutive.

In another embodiment, configuration of 3 and 5, and optionally 7positioning subframes for time aggregation of measurement samples may beallowed in addition to the use of 1, 2, 4, and 6 configured subframes.

In another embodiment, subframes used for the PRS(s) and measurementsare configurable over both 1 frame and 2 consecutive frames such thatthe set of subframes being used begins in one frame and ends in thenext. An example for TDD downlink/uplink (DL/UL) configuration 2 may besubframes 8 and 9 in one frame followed by subframe 0 in the next frame.

In another embodiment for TDD, only a subset of the DL/UL configurationsmay be configurable by the system to support PRS(s). For example, due tothe limitation of DL/UL configuration 0 having only subframes 0 and 5 asDL subframes, support of DL PRS(s) and the positioning methods requiringthese PRS(s) (for example observed time difference of arrival (OTDOA))may not be supported for configuration 0.

In another embodiment, as a function of the DL/UL configuration decodedby the WTRU in system information block (SIB) 2, the WTRU may consideras an error any positioning assignment that is inconsistent with thatconfiguration. For example, in the example above in which DL/ULconfiguration 0 does not support DL PRS(s), the WTRU would consider itan error if the WTRU decoded that the DL/UL configuration is 0 and thenetwork requested the WTRU to perform measurements on DL PRS(s).

In another embodiment, certain subframes in each frame may be designatedunavailable for PRS(s). The unavailable subframes may be pre-defined orsignaled to the WTRU. Examples of subframes that may be designatedunavailable are those containing system signals. For example, the methodmay disallow the assignment of subframe 0 and subframe 5 from beingassigned as positioning subframes. For FDD, the method may disallow theassignment of subframe 4 and/or subframe 9 from being assigned aspositioning subframes. For TDD, the method may disallow the assignmentof subframe 1 and/or subframe 6 from being assigned as positioningsubframes.

In another embodiment for TDD, special subframe configurations may carryPRS(s). The WTRU may consider as an error any positioning assignmentthat is inconsistent with the special subframes that may or may notcarry PRS(s).

In another embodiment, when normal subframes are used in TDD, PRS(s) maybe allowed in DL subframe 6, which is a subframe excluded from MBSFNallocations for TDD.

In another embodiment for TDD, a cell may be allowed to transmit DLPRS(s) in subframes designated as UL subframes (per the cell's DL/ULconfiguration) when that cell makes no UL allocations for that subframe(i.e., it issues no UL grants for that subframe) and either prevents (byappropriate scheduling of DL data transmissions), or ignores, ULacknowledgement/negative acknowledgement (ACK/NACK) transmissions inthat subframe.

Embodiments for subframe allocation configuration are disclosed herein.In all embodiments described herein, configuration may be provided tothe WTRU by signaling (e.g., radio resource control (RRC) signaling,physical layer signaling, and other similar signaling levels), possiblycombined with a priori known information (e.g., information fixed by thestandard). Signaling may include broadcast and/or dedicated signaling tothe WTRU.

In a first embodiment, if there are any subframes that may not be usedfor PRS(s) (referred to as unavailable subframes herein), the specifiednumber of “consecutive” subframes (in the configuration) would skip overthose subframes. This may be applied to both FDD and TDD.

The following information may, for example, be provided to the WTRU. TheWTRU may be provided with the frames that contain the PRS(s). Forexample, the frame allocation may be provided the same way the framesare defined for MBSFN, i.e., PRS(s) may occur in frames when systemframe number (SFN) mod P=Offset, where P is the periodicity of thePRS(s) in frames and Offset is a value in frames, so the allocatedframes become Offset, P+Offset, 2P+Offset, and so on. For the case wherethe PRS(s) cross into a second frame (as described herein), only theinformation for the first frame may need to be provided. The secondframe may be understood without additional information, (e.g., for theexample above, SFN mod P=Offset provides the first frame of the 2consecutive frames).

The WTRU may be provided with the starting subframe within the frame(e.g., an offset) and the number of consecutive subframes (wheresubframes that do not support positioning signals are skipped over). Forexample, in TDD configuration 2 with starting subframe 4 and theconsecutive subframes=4, if all DL subframes support PRS(s) and all ULand special subframes do not support PRS(s), this would correspond tosubframes 4, 5, 8, and 9. Subframe 6 may be skipped because it is aspecial subframe and subframe 7 may be skipped because it is an UL.

The number of consecutive subframes may instead be provided as a numberof additional consecutive subframes since the starting subframe may beunderstood to contain (or not contain) PRS(s) (e.g., based ondefinitions in the standard). For the example above, the number ofadditional consecutive subframes would be 3 (instead of 4 consecutivesubframes). The resulting subframes to use would be the same and onlythe value signaled to the WTRU changes.

In addition, the information provided may also allow for the possibilityof continuing in the next frame. For example, extending the examplesabove, in configuration 2 with starting subframe 4, consecutivesubframes=5 (or the additional consecutive subframes=4), and with all DLsubframes supporting PRS(s) and all UL and special subframes notsupporting PRS(s), this would correspond to subframes 4, 5, 8, and 9 inone frame and subframe 0 in the next frame.

Further, the unavailable subframes may be pre-defined, e.g., by thestandard, or signaled to the WTRU.

The unavailable subframes may be independent of, or a function of, theDL/UL configuration in TDD and/or other constraints in TDD or FDD.

The same signaling may be used in a FDD half-duplex mode, that is, forthose FDD WTRUs that cannot transmit and receive simultaneously.

In a first variation of the first embodiment, a number of bits, B, usedto signal the starting subframe and the number of consecutive (oradditional consecutive) subframes, N, may be limited to a small numberas described herein. For example, there are 10 subframes in a framewhich may be numbered 0-9. The starting subframe may be provided andlimited to a number less than 9 to reduce the number of bits used. Forexample, if the starting subframe were to be 0 to 7, this may limit thestarting subframe to 3 bits. The maximum value of N would dictate thenumber of bits needed for N. For example, if the maximum allowed valueof N were 7, only 3 bits would be needed for N. The configuration ofstarting subframe and which subframes to use may be accomplished in 6bits based on the example above.

In a second variation of the first embodiment, a number of bits, B, usedto signal the starting subframe may be an index, rather than an explicitstarting subframe number within the frame. The index may be based on asubset of the subframes in the frame such as the available subframes forpositioning signals. As an example, the maximum number of wholesubframes in a frame for TDD is 8. Rather than specify an explicitstarting subframe number from 0 to 9, which would require 4 bits, thestarting subframe number may be treated as an index from 0 to 7 into thelist of DL subframes allocated in the current configuration. Forexample, with configuration 4, a signaled start value of 6 would map tosubframe #9.

In a second embodiment, a bitmap is used to identify which subframes maycontain the PRS(s). The information provided to the WTRU may include theframes that contain PRS(s) as discussed herein and a bitmap to indicatewhich subframes are for the PRS(s). For example, for PRS(s) in a singleframe, a bitmap equaling 1001110100 would correspond to subframes 0, 3,4, 5, and 7. This may be extended to cover subframes in 2 consecutiveframes. A total of 10 bits may be used for each frame for a total of 20bits.

In a first variation of the second embodiment, less bits may be used tobe more efficient since the span will unlikely be more than 7 subframestotal. The worst case would therefore span the last subframe of thefirst frame and 6 subframes in the second frame, which would require atotal of 16 bits.

In a second variation of the second embodiment, given a startingsubframe, N bits may be used to represent the next N subframes, reducingthe number of bits needed. The following information may be provided tothe WTRU: a) the frames that contain the PRS(s) as discussed herein; b)the starting subframe number within the frame (i.e., an offset); and c)a bitmap to indicate which subframes are for the PRS(s), starting withthe subframe identified as the starting subframe.

In this variation, there may be 10 subframes in a frame which may benumbered 0-9. The starting subframe may be provided and limited to anumber less than 9 to reduce the number of bits used. For example, ifthe starting subframe were to be 0 to 7, this may limit the startingsubframe to 3 bits. The maximum value of N would dictate the number ofbits needed for N. For example, if the maximum allowed value of N were7, 7 bits would be needed for N. Note that depending on the definitionof N, it may include or exclude the starting subframe in the bitmap. Ifthe starting subframe is excluded, it would need to be known (e.g., bydefinition) whether PRS(s) are in that subframe or not. Based on theexamples above, the configuration of starting subframe and which nextsubframes to use may be accomplished in 3+7=10 bits.

In a third variation of the second embodiment, the number of bits, B,used to signal the starting subframe may be an index, rather than anexplicit starting subframe number within the frame. This may be based ona subset of the subframes in the frame such as the available subframesfor PRS(s).

In a fourth variation of the second embodiment, if there are anyunavailable subframes that cannot be used for positioning, the number ofbits used to convey which subframes to use automatically skips over theunavailable subframes. The unavailable subframes may be pre-defined,e.g., by the standard, or signaled to the WTRU. The unavailablesubframes may be independent of, or a function of, the DL/ULconfiguration in TDD or other constraints in TDD or FDD. For example,when 10 bits are used to represent 10 subframes, and if subframe 5 isunavailable, then no bit is needed for subframe 5. Therefore, 9 bitsinstead of 10 bits may be used. An example bitmap of 10011x0100, whichis using 1 to represent subframes to use for positioning and x torepresent the unavailable subframe 5, could be represented in 9 bits as100110100 and would correspond to designating subframes 0, 3, 4, and 7for positioning use. This may be applied to the other embodimentsdisclosed herein.

In a third embodiment, a number of consecutive (i.e., a span) ofsubframes may be provided, and the PRS(s) may only be in the availablesubframes within that span. The following information may be provided tothe WTRU: a) frames that contain PRS(s) as disclosed herein; and b) thestarting subframe within the frame (i.e., an offset); and c) the numberof consecutive subframes (where only the available subframes are usedwithin that span). For example, in TDD configuration 2 with startingsubframe 4 and consecutive subframes=5, if all DL subframes supportPRS(s) and all UL and special subframes do not support PRS(s), thiswould correspond to subframes 4, 5, and 8 (span is 4, 5, 6, 7, and 8,with subframe 6 not usable because it is a special subframe and subframe7 not usable because it is an UL).

In this embodiment, the number of consecutive subframes may instead beprovided as a number of additional consecutive subframes since thestarting subframe may be understood to contain (or not contain) PRS(s)(e.g., based on definition in the standard). For the example above, thenumber of additional consecutive subframes would be 4 (instead of 5consecutive subframes). The resulting subframes to use would be the sameand only the value signaled to the WTRU changes.

This embodiment also allows for the possibility of continuing in thenext frame. By extending the examples above, in configuration 2 withstarting subframe 4 and the consecutive subframes=7 (or the additionalconsecutive subframes=6), this would correspond to subframes 4, 5, 8,and 9 in one frame and subframe 0 in the next frame (span is 4, 5, 6, 7,8, 9, and 0, with 6 and 7 not usable since 6 is a special subframe and 7is an UL subframe).

The same signaling may be used in a FDD half-duplex mode, that is, forthose FDD WTRUs that cannot transmit and receive simultaneously.

In a first variation of the third embodiment, the first variation of thefirst embodiment (e.g., explicit values) may be applied to thisembodiment.

In a second variation of the third embodiment, the second variation ofthe first embodiment (e.g., index values) may be applied to thisembodiment.

In a fourth embodiment, a table may be defined where each row containsan index and a corresponding subframe allocation to be used for thePRS(s). The following information may be provided to the WTRU: a) theframes that contain the PRS(s) as discussed herein; and b) index intothe table that identifies which subframes to use, where i) index may bedependent on mode (FDD or TDD) and ii) index may be dependent on DL/ULconfiguration for TDD.

In a fifth embodiment, when MBSFN-reserved subframes are used forPRS(s), the maximum periodicity is currently 32 frames and may bemodified to include a frame periodicity of 64 or 128 frames. This may beimplemented by increasing the allowed periodicity of the MBSFN-reservedsubframe allocation to match the desired maximum periodicity of thepositioning subframes. For example, add 2 additional choices of 64 and128 frames.

In an alternative implementation, a mapping may be overlaid on top ofthe MBSFN-reserved subframe allocation and which allocations are to beused for PRS(s) are indicated. An example mapping may be to use everyother MBSFN-reserved subframe allocation or every 4^(th) MBSFN-reservedsubframe allocation to achieve a 64 or 128 frame periodicity for anMBSFN-reserved subframe allocation with a 32 frame periodicity.

Signaling this allocation to the WTRU may be accomplished by identifyingwhich MBSFN-reserved subframe allocation to use and what the overlaidmapping is. An example would be signaling 0 for every allocation, 1 forevery other allocation, 2 for every 4^(th) allocation, and so on.

Embodiments for methods that determine which subframes carry MBMS/MBSFNRSs are herein disclosed. In an embodiment, the WTRU supportingpositioning measurements such as PRS(s) determines which MBSFN allocatedsubframes contain MBSFN RS, or carry MBMS service. In an illustrativeexample of this embodiment, explicit signaling between network node(s)and WTRU(s) may be used to determine if PMCH data and/or MBSFN RS existsin an MBSFN allocated subframe. Information provided to the WTRU mayindicate that the PMCH data and/or MBSFN RS exist in the entire subframeor specific portions (e.g., RBs or REs) of the subframe. In anembodiment of this example, a WTRU supporting positioning measurementsdetermines from reading system information, either in the form ofbroadcast channel (BCH)/System Information Blocks (SIBs) or dedicatedradio resource control (RRC) signaling, whether one or more MBSFNallocated subframes contain MBMS and/or whether one or more subframescontain MBMS RS.

In another illustrative example of this embodiment, the WTRU performsblind detection to determine which MBSFN allocated subframes containMBMS and/or if they contain PMCH data and/or MBSFN RS.

It is known that if a MBSFN subframe has a MBMS signal, then automaticgain control is run on the control region and run again on the payloadregion. Described herein is an embodiment when a PRS is present in aMBSFN subframe. In this embodiment, if a PRS is present in the MBSFNsubframe, then the automatic gain control is run on the control regionbut not on the payload region. The automatic gain control from thecontrol region may be used for the payload region.

Embodiments for PRS sequences are disclosed herein. In one embodiment ofa PRS, polyphase sequences or constant amplitude zero auto-correlation(CAZAC) sequences (such as a Zadoff-Chu sequence) may be used for thePRS (no matter whether it is code division multiple access (CDMA) ororthogonal frequency division multiple (access) (OFDMA) type of signal).

In another embodiment of a PRS, M-sequence or other pseudo-randomsequences may be used for the PRS(s).

In yet another embodiment of a PRS, the common reference signals (CRS)in LTE Release 8 occupy scattered/staggered resource elements (REs) ineach subframe that may be extended to all REs in the subframe to be usedas superposed PRS(s). Alternatively, the PRS(s) may be a sequence whichbuilds on the CRS and allows the legacy CRS to be used withoutmodification as part of the PRS, while adding additional superimposedsignals over the data REs.

Although features and elements are described above in particularcombinations, each feature or element may be used alone without theother features and elements or in various combinations with or withoutother features and elements. The methods or flow charts provided hereinmay be implemented in a computer program, software, or firmwareincorporated in a computer-readable storage medium for execution by ageneral purpose computer or a processor. Examples of computer-readablestorage mediums include a read only memory (ROM), a random access memory(RAM), a register, cache memory, semiconductor memory devices, magneticmedia such as internal hard disks and removable disks, magneto-opticalmedia, and optical media such as CD-ROM disks, and digital versatiledisks (DVDs).

Suitable processors include, by way of example, a general purposeprocessor, a special purpose processor, a conventional processor, adigital signal processor (DSP), a plurality of microprocessors, one ormore microprocessors in association with a DSP core, a controller, amicrocontroller, Application Specific Integrated Circuits (ASICs),Application Specific Standard Products (ASSPs); Field Programmable GateArrays (FPGAs) circuits, any other type of integrated circuit (IC),and/or a state machine.

A processor in association with software may be used to implement aradio frequency transceiver for use in a wireless transmit receive unit(WTRU), user equipment (UE), terminal, base station, Mobility ManagementEntity (MME) or Evolved Packet Core (EPC), or any host computer. TheWTRU may be used in conjunction with modules, implemented in hardwareand/or software including a Software Defined Radio (SDR), and othercomponents such as a camera, a video camera module, a videophone, aspeakerphone, a vibration device, a speaker, a microphone, a televisiontransceiver, a hands free headset, a keyboard, a Bluetooth® module, afrequency modulated (FM) radio unit, a Near Field Communication (NFC)Module, a liquid crystal display (LCD) display unit, an organiclight-emitting diode (OLED) display unit, a digital music player, amedia player, a video game player module, an Internet browser, and/orany Wireless Local Area Network (WLAN) or Ultra Wide Band (UWB) module.

What is claimed is:
 1. A wireless transmit receive unit (WTRU)comprising: a transceiver and a processor configured to receive areference signal of a first type; wherein the first type is other than acell specific reference signal (CRS), an Multicast Broadcast SingleFrequency Network (MBSFN) reference signal or a demodulation referencesignal (DM-RS); and wherein reference signals of the first type arereceived in resource elements other than resource elements used for aphysical broadcast channel (PBCH), a primary synchronization signal or asecondary synchronization signal; and the transceiver and the processorare further configured to receive a radio resource control messageindicating a subframe position in which the reference signal of thefirst type is transmitted and a periodicity of a transmission of thereference signal of the first type, and a number of antenna ports for atransmission of the reference signal of the first type.
 2. The WTRU ofclaim 1, wherein resource elements of the reference signal of the firsttype are not received in a first three symbols of a subframe.
 3. TheWTRU of claim 1, wherein the reference signal of the first type is apositioning reference signal.
 4. The WTRU of claim 1, wherein resourceelements of the reference signal of the first type are not resourceelements used for CRS.
 5. The WTRU of claim 1, wherein the referencesignal of the first type is derived from a pseudo-random sequence.
 6. Amethod performed by a wireless transmit receive unit (WTRU) comprising:receiving a reference signal of a first type; wherein the first type isother than a cell specific reference signal (CRS), an MulticastBroadcast Single Frequency Network (MBSFN) reference signal or ademodulation reference signal (DM-RS); and wherein reference signals ofthe first type are received in resource elements other than resourceelements used for a physical broadcast channel (PBCH), a primarysynchronization signal or a secondary synchronization signal; andreceiving a radio resource control message indicating a subframeposition in which the reference signal of the first type is transmittedand a periodicity of a transmission of the reference signal of the firsttype, and a number of antenna ports for a transmission of the referencesignal of the first type.
 7. The method of claim 6, wherein resourceelements of the reference signal of the first type are not received in afirst three symbols of a subframe.
 8. The method of claim 6, wherein thereference signal of the first type is a positioning reference signal. 9.The method of claim 6, wherein resource elements of the reference signalof the first type are not resource elements used for CRS.
 10. The methodof claim 6, wherein the reference signal of the first type is derivedfrom a pseudo-random sequence.
 11. The WTRU of claim 1 wherein thetransceiver is configured to transmit information based on the receivedreference signal of the first type.
 12. The method of claim 6 furthercomprising transmitting information based on the received referencesignal of the first type.